The objective of this study is to test agents for efficacy to inhibit prostate cancer male Wistar (cpb:WU) rats 5-6 weeks of age are being pretreated with cyproterone acetate by gavage at 50 mg/kg body weight daily for 18 days. One day after the last cyproterone acetate dose animals receive a single s.c. injection of testosterone propionate at 100 mg/kg body weight. Sixty hours after the testosterone injection the animals are being inoculated i.v. with MNU (30 mg/kg body weight) at 5-6 weeks of age. On the day after MNU injection each rat receives, s.c., two implants of 40 mg of crystalline testosterone in a capsule of silastic membrane, which is repeated at intervals of 6 months. Animals are being fed either control diets or diets containing the chemopreventive agent from one week prior to MNU treatment to the end of the study. All rats are weighed and average food consumption determined weekly. Each rat is palpated weekly for the appearance of prostatic masses, beginning at 6 months of age. The animals are sacrificed if they appear moribund and necropsied. Three animals from each of the treatment and the control groups are being sacrificed periodically for assessing blood hormone profiles and histological changes in the prostate. When rats develop a palpable tumor, are moribund, or at 12 to 14 months after initiation of the experiment, These animals are sacrified and examined for gross and microscopic prostate tumors and other lesions as described. The tissues are prepared a blinded manner for pathological diagnosis by an experimental animal prostate cancer expert. The agents being studied include: Soy Protein Extract, BBI, a lipoxygenase inhibitor, and an androgen blocker .